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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

How does Arctic sea ice loss compare to Antarctic sea ice gain?

What the science says...

Arctic sea ice loss is three times greater than Antarctic sea ice gain.

Climate Myth...

Arctic sea ice loss is matched by Antarctic sea ice gain
In fact, the global sea-ice record shows virtually no change throughout the past 30 years, because the quite rapid loss of Arctic sea ice since the satellites were watching has been matched by a near-equally rapid gain of Antarctic sea ice. Indeed, when the summer extent of Arctic sea ice reached its lowest point in the 30-year record in mid-September 2007, just three weeks later the Antarctic sea extent reached a 30-year record high. The record low was widely reported; the corresponding record high was almost entirely unreported. (Chris Monckton)

Have Arctic ice losses truly been balanced by Antarctic gains? The first point to clarify is that we are talking about floating sea ice, not to be confused with land ice. Land ice at both poles and in glaciers around the world is sliding into the ocean at an accelerating rate. This net loss of land ice is contributing to sea level rise.

However, Monckton is clearly referring to sea ice. The rapid decline of Arctic sea ice has indeed coincided with an increase in Antarctic sea ice. But do these two opposite trends cancel out as Monckton suggests? In reality, the upward Antarctic trend is only slight compared to the plummeting Arctic trend. Tamino has crunched the numbers and found the Arctic trend is in fact more than three times faster than the Antarctic one. The net result is a statistically significant global decrease of more than a million km2 or a few percent – would you agree with Monckton that this is “virtually no change”?

Summer and Winter, Apples and Oranges

Monckton compares the Arctic summer to the Antarctic winter, not the most appropriate comparison. Sea ice grows and shrinks seasonally because polar latitudes have vastly more daylight hours in summer than in winter. When ice melts, it makes the surface less reflective and amplifies the warming (as is currently occurring in the Arctic), but this effect can only make a difference when the Sun is up. Thus the most important time of year for sea ice is its annual minimum which occurs at the end of the summer: September in the Arctic but February in the Antarctic.

While the summer Arctic has lost an extent of about 2.5 million km2 (equivalent to the area of Western Australia), the summer Antarctic growth is only 0.3 million km2 (about the size of Victoria). Even that slight upward trend is less than the year-to-year variability; although 2003 and 2008 tied for the highest February extent, 2006 was third lowest. Again, the real world contradicts Monckton’s assertion that changes in the Arctic are being balanced out by the Antarctic.

The Third Dimension

Furthermore, Monckton fails to mention that Arctic sea ice is not only shrinking in extent but also has been thinning rapidly. Although its lowest extent was in 2007, its volume has continued declining since then, hitting another record low in 2010:

Meanwhile there has been a slight increase in Antarctic sea ice volume, but only by about 5,000 km3 (insufficient to offset the Arctic decline shown in Figure 4), and most of it in a few years at the start of the record.

Comments

Hope I've got the right thread here. I recently had an online discussion with a 'skeptic' in which he claimed that 'skeptics' only talk about sea ice extent because the measurements for volume are unreliable. I duly did my research and, as I expected, his criticisms were invalid. Measurements are taken by satellite, submarine, and by scientists on the ground,then extrapolated for the whole area of coverage. From what I read the results are reliable, in fact slightly overestimating the thickness of the ice. However, two days ago I read a newspaper article in which the chief scientist at the met office was quoted as saying that the thickness of arctic sea ice is not known with any confidence.
http://www.guardian.co.uk/environment/2012/mar/14/met-office-arctic-sea-ice-loss-winter
This has left me slightly baffled and perplexed. I just wondered if anyone would like to try and shine a light on this for me. Thanks.

Thanks for the link. From the discussion at Nevens its clear that Ms Slingos comments seem to be odds at what other scientists are saying. But I should imagine that her comments will be used by 'skeptics' to justify their exclusion of ice volume measurements and, in this case, they can point to a credible source to back up their argument.

The data presented above is outdated by a few years. The combined anomoly of NH and SH sea ice is trending upward since 2007. As electric rates have risen 40% over the last 7 years, justification has thinned more than the ice has.

However, the Arctic ice volume 2014 peak is lower than the 2007 peak, but by a very small amount, far less than 1000 cubic km (PIOMAS). I'm not seeing the Arctic sea ice decrease on the order of 'three times as much as' in recent data. Things are different than in July 2012. This year has seen the remaining Arctic ice exceed seven other recent years just since April 22nd (Charctic), due to slow spring 2014 melt and the remaining Arctic ice is only 5.4% less than this time in 1994. As a comparison, 1994 was a very cold winter as I moved from S. Fla to Indiana at the start of that deadly winter. The temp at my apartment hit -44F without the wind chill on MLK day. I considered the possibility that the cold air over the great plains that day contracted the U.S. such as to have caused the Oakland earthquake that same day. As I recently have read about ocean volume thermal expansion due to surface temp increase, it might not have been so far fetched a thought.

Response:

[PS] This moderator is struggling to decide whether you actually cant understand that cherrypicking and short trends are not science or whether you are trolling. You have been called on this before.

1) Use of short time span for comparison? Only eight years of a 30 plus year record used. Check!

2) Use of previous record breaking year as start point for comparison? 2007 record year used. Check!

Well, your certainly playing from the denier play sheet for bad science.

Trying to turn an April PIOMAS which is less than the trend value into evidence that the trend is reducing certainly shows gumption, but surely you must know that such unethical distortions of the facts will get called on this site:

Response:

[PS] Jetfuel, please ackowledge that you understand Tom's point. If you dont understand, then more explanation is likely to be offered. If we get a "look, squirrel" instead, then your posts will be deleted.

The cherry-picked number,Δ(Arctic Sea Ice Volume maximum 2007 & 2014), described as "a very small amount, far less than 1000 cubic km (PIOMAS)" is 750 km3, which over a seven year period and in the units used in the graph @5 represents a trend of -1.07 (1000 km3/Decade). It isn't a very ripe cherry.

The comparison presented @4, that of Arctic Sea Ice loss being allegedly not "on the order of 'three times as much as' in recent data," it is a comparison with Antarctic Sea Ice gain. Antarctic Sea Ice Volumes are not as well understood as their northern equivalents, but Holland et al (2014) suggest an Antarctic Sea Ice Volume trend of +0.3 (1000 km3/Decade) for 1992-2010. Ironically, that is about a third the size of the cherry-picked measure of ice loss in the Arctic.

I do wonder if the attempt by jetfuel@4 to challenge the assertion made in this post (that Antarctic Sea Ice is growing at a much slower rate that Arctic Sea Ice is shrinking) should be batted away innto the long grass simply because of the incompetence of jetfuel to state his case.

It is true that over the satellite record (1979 - to date), the decline in Arctic Sea Ice Area & Extent is roughly three times larger than the increase in Antarctic Se Ice Area & Extent. It is also true that both the Arctic decline and the Antarctic increase - both these trends have shown signs of acceleration over recent years, yet generally the three-to-one ratio remains. And it is true that the acceleration in trends is accompanied by greater variability but this has not resulted in net global Sea Ice area & extent anomalies reaching any unprecedented values* when examined as daily, monthly or quarterly averages, *unprecedented taken as values over the last decade, there being variability evident with such periodicity.However, recent Net Global Sea Ice area & extent do start to show unprecedented values* when Annual Averages are examined. This results mainly from the Antarctic anomaly showing a rising trend over the last two years. While this remains presently a short-term phenomenon, the mechanisms behind the growth of Antarctic Sea Ice area & extent are known to be the product of Antarctic regions with increasing sea ice cover and other Antarctic regions with decreasing sea ice cover. The net Antarctic anomaly is the result of two far larger values that presently come close to cancelling each other out. Such a cancellation cannot be relied on. One of the mechanisms (for increase or decrease) could easily come to dominate the anomaly in future decades, as may have been the case prior to the satellite era. Indeed, Fan et al (2014) argue quite convincingly that the start of the satellite data (1979) likely coincides with a shift from significant Antarctic summer (DJF) ice loss over the period 1950-78.Thus, while the comments by jetfuel are based on cherry-picking nonsense, and while the Net Global Sea Ice area & extent has been in decline over the satellite era (1979 - to date), predicting a continuation of that decline is potentially foolhardy as future trends, in particular Antarctic Sea Ice cover, remain uncertain.

The data in figure 2 is a 12 month average, not the maximun. The Antarctic sea ice maximun (this year) was just over20 million km2. Sea ice was only that high for about one week. Sea ice has dropped to about 18 million km2. The yearly average is lower than the maximum is. The graph is also from last year so it does not include the most recent data.

The yearly average is more informative than the maximum because it tells us about what is happeing the entire year. A graph of all the data can be found here (the graph is area not extent so the maximun this year is 17 million km2. The graph of the Antarctic is about half way down the page.)

I got into an argument recently with a denier who is convinced the gain of seasonal Antarctic sea ice compensates for the loss of Arctic sea ice, because the increased albedo in the south substitutes for the loss of albedo in the north. I worked up a graphic to show why that doesn't work.

Below is a picture of the Earth in northern hemisphere summer. This is the time that the Arctic ocean under the collapsing northern sea ice is absorbing the most heat from the sun. This is also the time of the greatest extent of Antarctic sea ice, since it is winter in the southern hemisphere. This is the time of year when deniers claim the minor increase in seasonal Antarctic sea ice somehow compensates for the loss of permanent northern sea ice.

The red streak at the top of the picture shows the amount of sunlight falling on the vanishing northern ice cap. The thin red line at the bottom of the picture shows the amount of sunlight falling on the “increased” southern hemisphere sea ice. Both are approximations. In the north, I enclose the entire ice cap, not just the parts that have vanished, because in a very few years the Arctic will be virtually ice-free in the summer. Likewise, I made the southern line about three times thicker than it should be, to allow for three times as much Antarctic seasonal sea ice gain than we’ve seen so far, so that deniers don't think I'm ignoring the possibility of more growth there.

As you can see, the two red patches are not anywhere near the same size. The loss of Arctic sea ice cannot be compensated for by a gain in Antarctic winter sea ice, unless Antarctic winter sea ice begins to reach to Madagascar and to southern Australia.

This graphic is only approximate. It may be more useful (and more complete) to do a series of more carfully-made graphics, starting with polar views that show both the average and the current extent of Arctic summer and Antarctic winter sea ice, and then probably a picture showing where the sun rays fall in September when the Arctic is at its minimum and the Antarctic is at its maximum. Probably also, the final graphic should be from the sun's point of view, showing the vast areas of now-open ocean lit by the sun in the north, and the thin sliver of arc where the Antarctic "increase" is located.

If this does seem to be a useful approach, feel free to either adapt this graphic, or to request the series.

All this ignores, of course, the fact that whatever happens near the South Pole can't possibly undo the changes to northern hemisphere climate (wind and ocean currents, loss of habitat, etc.) that the loss of Actic ice causes.

Isn't the situation just the reverse six months later, when it is Southern hemisphere summer? I would think, that if the ice gain in the South were equal to the ice loss in the North there would be no change in albedo fo Earth as a whole over the year.

Rovinpiper @11, not it is not. That is because the Arctic is an ocean surrounded by land, while the Antarctic is land surrounded by ocean. The important effect of that is that while in principle summer sea ice in the Arctic can shrink to zero, thereby exposing the entire Arctic ocean with its much lower albedo than sea ice; the Antarctic sea ice shrinking to zero still effectively left the entire polar region above 70 degrees south covered by land ice, and hence maintaining the same albedo. As the Arctic sea ice shrinks will within that 70 degree circle, the consequence is a much larger Arctic impact on seasonal albedo.

bozza @13, there are three different things that could be meant by a claim that the NH is 'warmer than' the SH.

First, it might be a claim that the annual variation is surface temperature is greater in the NH than in the SH, as shown in this chart:

This greater variation results in the seasonal variation in global mean temperatures being in phase with the NH variation, even though the SH in fact recieves more sunlight over the year. The reason for this difference is the relatively low thermal inertia of the NH (which is 39% land) compared to the SH (which is only 19% land).

The same factor is the dominant factor in the more rapid rise in mean hemispheric temperatures in the NH since 1950 (the second possible interpretation), shown here:

Neither implies that the NH is actually warmer than the SH in absolute terms, as a more rapid warming response also implies a more rapid cooling response. In fact, it appears that in absolute terms, the SH is warmer than the NH:

"Data from a large number of stations suggest that the annual mean temperature is around 27o C within 20o S - 16o N degrees and then falls by about 0.85 K/degree latitude in the northern hemisphere and 0.63 K/o lat in the south (Fig 2). This implies that on average the southern hemisphere is warmer than the northern hemisphere (17oC vs 11oC, respectively), which is true, if the Antarctic plateau stations are excluded, as in Fig 2. These stations are 30-40K colder than the curve in Fig 2 suggests, on account of their altitude and their isolation within the circumpolar vortex."

It may be that the very cold Antarctic temperatures more than compensate for the greater extent of tropical warmth in the SH, and the slower loss of temperature with higher latitude. But I have no evidence showing that to be the case.

Regardless, the cause of these differences are complex, including the effect of the positions of landmasses and currents on the location of the Inter Tropical Convergence Zone (which would govern the latitudinal extent of the tropical zone) and the relative ease of heat transport towards the poles in the two cases. Part of the explanation may lie in the circumpolar vortex around Anarctica, which by limitting heat transport to the pole may allow that heat to remain in mid-latitudes in the SH rather than being transported to the pole (or at least above the arctic circle) in the NH.

Ok, so why is the fact that there is land at the South Pole so important? Ice can melt on land, too. Open ocean absorbs heat very well, but what is the rock of Antarctica like? How well will it absorb heat?

The really big factor is height. The south pole is at 2700m - making it a much colder place than North pole. Raising the summer temperature from current -29C to say -9C still wouldnt do much melting. Furthermore, arctic ice is constantly moving with combination of wind and currents. Moving ice from somewhere cold to somewhere warm is much more effective at melting than inplace melting. In the antarctic, ice movement is at literrally glacial pace. The oceans also bring in warmer water which thins arctic ice but so far only affects the antarctic margin.

Rovinpiper @15, the coroilis effect leads to circular patterns of motion in air and sea currents because the coroilis "force" is always at right angles to the direction of motion of the wind or sea current, as illustrated below:

Around the north and south poles, this leads to a permanent circumpolar vortex which helps prevent the flow of warm are from the south above the Arctic or below the Antarctic circle. There are differences between them. Specifically:

"Large hemispheric differences in the polar vortices can be seen in Figure 1: The Antarctic vortex is larger, stronger (more rapid westerlies), and has a longer lifespan than its Arctic counterpart. These differences are caused by hemispheric differences in the wave generation and propagation. The larger topography and land-sea contrasts in the NH excite more/larger planetary-scale Rossby waves that disturb the stratospheric vortex and push it farther from radiative equilibrium than in the SH. The hemispheric differences in the strength and, in particular, coldness of the polar vortices are extremely important for understanding ozone depletion, as explained below."

Because the Antarctic polar vortex is larger, it keeps the warm air further from polar regions. Because it is stronger, it more effectively insulates Antarctica. Further, because the Arctic polar vortex is less stable, it often moves far from its central position with the effect that frigid air is brought into temperate regions, and warm air is pumped into the Arctic.

The difference is stability is a direct consequence of the fact that the Arctic is water surrounded by (very cold in the winter) land, whereas the Antarctic is land surrounded by relatively warm water.

More important than the atmospheric polar vortex are the circumpolar currents found around Antarctica (also caused by the coriolis effect), which limit the ability of warm water from reaching the coastline of Antarctica.

Obviously these circumpolar currents are only able to form because Antarctica is land surrouned by water. In the NH, no such currents form. Instead , the Eurasian landmass diverts part of a tropical current (the Gulf Stream) north, carrying warm water deep into the Arctic ocean. There is also a smaller, seasonal warm current through Berring Strait:

The effect of this is two fold. First the Norwegian Current (the extension of the Gulf Stream) keeps waters as far north as Svalbad unfrozen in winter in the North Atlantic (in current conditions). Second, because the water enters the Arctic ocean at the Norwegian current, it must exit somewhere else, and much of it exits in two cold currents flanking Greenland (part of the reason Greenland has preserved it's ice sheet).

This difference in ocean currents is the primary factor in differences in heat transport to the poles, which in turn is a major factor in the difference between Arctic and Antarctic ice levels.

There are additional factors, including the facts that:

The Antarctic ice shelf has a very high altitude leading to a substantial cooling of the interior.

When ice forms in the Arctic ocean, the remaining water is hypersaline, causing it to be very dense, and consequently sink. That in turn carries the cold water away from the bottom of the ice, drawing in warmer water from further south - a factor which limits the depths to which ice can form.

Liquid water cannot exist much below 0oC. In contrast, the earth and rock can drop to much lower temperatures. That means the Arctic ice, sitting over water cannot be much cooler than 0oC (although the air mass above it in winter, which is insulated by snow from the ice, can be). In constrast, land ice on Antarctica and Greenland can fall to much lower temperatures.

Even where the ice does melt, rock and soil typically have a much higher albedo than does open water (although given the thickness of the land ice involved, this is a very minor factor).

Of the five factors (ie, difference in heat transport plus the four listed above), it is not clear as to their relative importance, although I think the evidence is stronger for the differences in heat transport being most important (and overwelhming that item 4 in the list is the least important).

bozza @19, there is a coriolis effect in the NH just as in the SH, and vice versa. What causes that effect to have different consequences in the SH than in the NH is the different distributions of land and water; which also has other consequences on climate independent of the coriolis effect. So if you want to reduce it to a simple formula; the NH polar regions are warmer than the SH polar regions because the Arctic is water surrounded by land, while the Antarctic is land surrounded by water. Differences in distribution of land and water also explains the more southerly location of the tropical zone, and the slower loss of temperature with latitude in the SH temperate zone relative to the NH temperate zone.

That said, it is a mistake to reduce things to that level of simplicity. When you do, deniers swoop in and pick out a minor factor claiming it was "ignored by climate scientists" and that "it is the real cause". And although those claims are rubbish, depending for their rhetorical effectiveness on people not having had those other factors discussed before hand, by oversimplifying the scientific story we are just setting people up for those pseudoscientists.

I know it would be a massive project, but I respectfully suggest combing through these excellent "rebuttal" pages and updating them. Several were written years ago, and there is more data now.

The arguments haven't changed, but the graphs and text could be updated to reflect newer data. For example, there have been new sea ice record lows since this article was written.

I know deniers who will whine that things have changed since c. 2011, that trends have "reversed", that sea ice is "recovering". It would be useful, for all the rebuttal pages, to update the data to show these denialist arguments to be as senseless as they are.

Response:

[JH] Updating the rebuttal articles is a priority activity for the all-volunteer SkS author team in 2016.